The Ninth Battle of Iserlohn (Japanese: 第9次イゼルローン攻防戦) was the first phase of Duke Reinhard von Lohengramm's Operation Ragnarök, a diversionary attack by the Galactic Empire against Iserlohn Fortress to distract the Free Planets Alliance from the Imperial invasion through the Fezzan Corridor. After the kidnapping of Emperor Erwin Josef II in the summer of 798 UC(489 IC / 3598 CE) and his reappearance in the Alliance at the head of a "legitimate" government-in-exile, Imperial prime minister Reinhard von Lohengramm devised a plan to invade the Alliance. Operation Ragnarök hinged on the bulk of the Imperial Fleet passing through and entering the Alliance using the demilitarised Fezzan Corridor, but an initial assault on Iserlohn Fortress was launched to ensure that Alliance politicians continued to believe that the Imperial invasion would be through the Iserlohn Corridor.

High AdmiralOskar von Reuenthal led an Imperial fleet that laid siege on Iserlohn Fortress in November 798 UC(489 IC / 3598 CE) and kept the Alliance's premier fleet, the Yang Fleet of Admiral Yang Wen-li, tied up at Iserlohn for over a month. In the meantime the Empire annexed Fezzan and entered Alliance space. At that point the defenders chose to abandon the fortress to the Imperial forces, with the Yang Fleet evacuating and returning to Alliance territory.

The summer of 798 UC(489 IC / 3598 CE) saw the kidnapping of the young emperor Erwin Josef II in a scheme organised by Fezzani leader Adrian Rubinsky and the creation of a government-in-exile of former high nobles in the Alliance, with the aim of overthrowing Duke Reinhard von Lohengramm's regime in the Empire. The Fezzanis convinced or persuaded Trunicht and his administration to accept the exiles. As Rubinsky intended, this gave Lohengramm a reason rally the people and declare war on the Alliance. The Imperial dictator's invasion plan, Operation Ragnarök, called for a diversionary attack on Iserlohn while the majority of the Imperial Fleet annexed Fezzan and proceeded to invade the Alliance through the Fezzan Corridor. This way they could avoid dealing with Yang Wen-li and Iserlohn Fortress directly. With the assistance of defected Fezzani ambassador Nikolas Boltik, Lohengramm decided to enact the plan. (LOGH: 'Lost Things', 'Determination and Ambition', 'The Arrow Is Released', 'Operation: Ragnarök')